Sulfur trioxide and sulfuric acid are important basic chemical raw materials. Currently, the process for producing sulfuric acid generally includes two steps: the first step comprises producing sulfur dioxide by the combustion of sulfur, by the calcination of pyrite, or by the decomposition of gypsum under reducing atmosphere; and the second step comprises oxidizing the produced sulfur dioxide into sulfur trioxide at a high temperature under the presence of catalyst, absorbing sulfur trioxide by concentrated sulfuric acid, and then producing sulfuric acid with a concentration as required. The above process for producing sulfur acid is of complex operation, high cost in investment and operation, and high energy consumption. Especially, it results in a serious environmental pollution.
Thermal decomposition of pyrosulfate is generally used as the existing process for producing sulfur trioxide in the laboratory. However, it is difficult to control the operation conditions of the process, and the producing cost is high. Also, the process is difficult to be used in mass production.
Besides, there is an increasing lack in natural sulfur and pyrite, whereas the reserves of natural gypsum are large. In particular, industrial waste gypsum, which is in a very large amount, has not been sufficiently recycled, and further leads to a serious environmental pollution.